Effects of combustor geometry on hydrogen–air premixed flame combustion in an annular microcombustor

Abstract

Heat losses at the walls and heat release are two competitive rate processes in microcombustion, and a microcombustor design must balance them appropriately for optimal performance. The primary objective of this work was to study the effects of some design variables on the processes influencing microcombustor characteristics and performance. A new compact and lightweight premixed hydrogen–air annular microcombustor was studied using a detailed computational fluid dynamics model validated against experimental data from literature. Heat reflux and flame stabilization were achieved by inserting a hollow tube in the combustion zone, which was also thermally isolated to reduce heat losses. It was found that the flame structure was insensitive to the thickness of inner tube, while wall temperature was not. On the other hand, a compact flame was obtained for larger aspect ratios, and wall temperature field did not alter significantly. Performance improved marginally with a higher thermal conductivity hollow tube. However, larger aspect ratio resulted in inferior thermal performance and non-isothermal walls. Thus, a configuration with smaller aspect ratio and thin-walled inner tube, possibly with a high thermal conductivity, was found to be desirable for good thermal performance. Finally, the model predictions indicated suitability of the design for intended applications.